A. Field of the Invention
The present invention relates to a new and improved high speed chuck that includes a locking mechanism for locking the workpiece gripping jaws in position preventing movement of the jaws due to centrifugal force developed during rotation of the chuck.
B. Description of the Prior Art
For many machining operations the workpiece being machined is rotated by a rotary chuck that includes radially movable jaws for gripping the workpiece. Because the jaws are radially mounted, they are urged to move outwardly by centrifugal force as the chuck is rotated at increasing angular velocities thereby tendint to loosen the gripping force of the jaws on the workpiece. This action results in a possible situation in which the workpiece may be released while being rotated at a high angular velocity.
To counterbalance the centrifugal force, prior art chucks employ a centrifugal counterweight. The counterweight typically is in the form of a lever mechanism that is mounted on the chuck such that as the rotational angular velocity increases, the lever pivots to apply a radially inward force on the jaw that increases with the increase in angular velocity.
The intention of these prior art devices is to counterbalance the outward centrifugal force on the jaw assembly with equal and opposite inwardly directed force. This necessitates a delicate counterbalancing. For particular installations it may be possible, in theory, to compensate exactly for the forces such that the net force on the jaws cancels out and the jaws are able to hold the workpiece with equal force at all rotational velocities. This, however, can not be uniformally accomplished for each different installation since each requires different jaw types. Accordingly, the only practical alternative available in the prior art is to overcompensate for the centrifugal forces. This prior art approach involves applying a radial force that is always larger than the centrifugal force tending to push the jaws outwardly away from the workpiece.
The net inward force in this prior art procedure is a function of the angular velocity at which the chuck is rotating. The faster the chuck is rotated the greater the force acting on the jaws to push them inwardly. This creates the problem that if the workpiece is thin-walled, the jaws can actually crush the workpiece.
Examples of the employment of levers or similar devices to provide a radially directed counteracting force is disclosed in the following U.S. Pat. Nos. 3,984,114, 3,751,053, 2,828,134, and 2,982,558.